Conventional novolac resins, prepared from phenolic compounds such as phenol and a source of formaldehyde, in the presence of strong acid catalysts such as sulfuric acid or hydrochloric acid or oxalic acid, are characterized by having a preponderance of para/para and ortho/para methylene bridges as illustrated below. ##STR1## whereas the so-called "high ortho" novolac resins are characterized by having mostly ortho/ortho methylene bridges as illustrated below: ##STR2## the main advantage of the "high ortho" novolac resins being the much greater speed of cure when reacted with hexamethylenetetramine. "High ortho" novolac resins are commonly prepared by reacting phenolic compounds such as phenol and a source of formaldehyde in the presence of either a divalent metal oxide (e.g. MgO and ZnO) or an organic acid salt of a divalent metal (e.g. zinc acetate or magnesium acetate) catalyst system. This invention relates to the production of so-called "high ortho" novolac resins, which are identifiable as being heat-hardenable phenol-formaldehyde resins of enhance hardening speed.
U.S. Pat. No. 3,476,707 by H. M. Culberton has disclosed that in the production of novolac resins, a catalyst system comprising (1) an oxide or hydroxide or organic acid salt of a divalent electropositive metal, and (2) a halogen acid or halide of a divalent electropositive metal, is particularly effecting in promoting "high ortho" orientation in the formation of the resins, with a significant increase in yield and lowering of processing temperature.
Such high ortho novolac resins have ortho orientation of from about 50 to 75% being produced under aqueous conditions.
It has now been discovered that high ortho resins can be produced having high ortho orientation of from about 75 to 100% in an improved process. The invention relates to an improved process for preparing very high ortho novolac resins, said process including reacting phenol and formaldehyde in the presence of a divalent electropositive metal oxide, hydroxide or organic salt wherein the improvement comprises conducting said reaction with said catalysts in combination with a divalent electropositive metal salt selected from the group consisting of sulfonates and fluoroborates or acids selected from the group consisting of sulfonic and fluoroboric or mixtures thereof. Such very high ortho novolacs have the technical advance of being heat-hardenable with greatly enhanced hardening rates as bonding resins.